Merge pull request #1854 from OceanParcels/docs_drop_jit

Documentation page on rationale for dropping JIT in Parcels v4

Author: erikvansebille

docs/v4/index.md

@@ -9,5 +9,6 @@ Collaboration on v4 development is happening on the [Parcels v4 Project Board](h
 ```{toctree}
 
 api
+nojit
 Parcels v4 Project Board <https://github.com/orgs/OceanParcels/projects/5>
 ```

docs/v4/nojit.md

@@ -0,0 +1,16 @@
+# Rationale for dropping JIT support in v4
+
+Parcels v4 will not support Just-In-Time (JIT) compilation. This means that the `JITParticle` class will be removed from the codebase. This decision was made for the following reasons:
+
+1. We want to leverage the power of `xarray` and `uxarray` for data handling and interpolation. These libraries are not compatible with the JIT compilation in v3.
+2. We want to make the codebase more maintainable and easier to understand. The JIT compilation pre-v4 adds complexity to the codebase and makes it harder to debug and maintain.
+3. We have quite a few features in Parcels (also v3) that only work in Scipy mode (particle-particle interaction, particle-field interaction, etc.).
+4. We want users to write more flexible/complex kernels. JIT doesn't support calling functions, or using methods from `numpy` or `scipy`, while this is possible in Scipy mode.
+
+Essentially, the only advantage of JIT was its speed. But now that the ecosystem for just-in-time compilation with python has matured in the last 10 years, we want to leverage other packages and methods (`cython`, `numba`, `jax`?) and Python internals for speed-up.
+
+Furthermore, we think we have some good ideas how to speed up Parcels itself without JIT compilation, such as relying more on vectorized operations.
+
+In short, we think that the disadvantages of JIT in Parcels v3 outweigh the advantages, and we want to make Parcels v4 a more modern and maintainable codebase.
+
+In our development of v4, we will first focus on making the codebase more modular and easier to extend. Once we have a working codebase, we will release this as `v4-alpha`. After that, we will start working on performance improvements.